If Operation Olympic had been launched, would a diversionary force filled with AA guns have been launched at least a week prior to wreck most of the Japanese kamikazes that were to attack the ships.
Yeah I think Richard Frank is the authority on this, and he argues in his book that the only real landing spot that the Americans could have hit and avoided a bloodbath was northern Honshu. The Soviets caught the Japanese completely by surprise and they would have been unable to rapidly shift forces north if the war continues past mid-August.
Despite all this, if the US lands in the teeth of the Japanese defenses in Kyushu or central Honshu then a diversionary attack would be very useful.
The Soviets may also be content to let the Americans have to fight a large-scale battle and to fight the amphibious war in the supporting role for a change. Japanese strategy involved Festungen and poorly-armed levies that were armed mobs, and that against the guys who orchestrated Bagration is asking for a whupping.
The USA would have as much difficulty here as it did in other large-scale engagements, which it had relatively few of in WWII. Japan can't win, but it can inflict Wacht Am-Rhein style embarrassments.
The key is whether good ol' Douglas MacArthur changes the invasion plan due to intelligence figuring out the Japanese are prepared for both Olympic and Coronet. I fear the worst for the US.